[gdal-dev] Can I change SOURCE_EXTRA setting at compile time?

[Roger André]

Hi Frank,

I've theorized all sorts of reasons for what I'm seeing.  So far none of
them are right.  Basically, if I take a really high-res epsg:4326 image, and
serve it up through Mapserver in epsg:900913, there are instances where I
get images back which are missing rows of pixels at the bottom of the
image.  If I reduce the resolution of the image the lines go away.  I
haven't yet figured out at what resolution the problem starts to appear.

I just tested the idea of changing the values in the warper code:
First:
nResWinSize += 100;
Then:
nResWinSize += 500;

Then rebuilt gdal.   Didn't seem to make a difference.

Thanks for the info though.

Roger
--

On Tue, Nov 18, 2008 at 5:07 PM, Frank Warmerdam <warmerdam at pobox.com>wrote:

> Roger André wrote:
>
>> I've been mercilessly beating a dead horse on a couple of lists about some
>> weird artifacts that I'm getting when doing reprojections in Mapserver from
>> epsg:4326 to epsg:900913.  It's recently come to my attention that something
>> was discussed in an IRC chat that might be pertinent to this issue, and I
>> was hoping I could test it.  Specifically, it relates to SOURCE_EXTRA, and
>> although the conversation at the time dealt with issues at the International
>> dateline, I think it might also manifest itself in other edge cases (literal
>> edges). ;).
>>
>> I would like to know if it is possible to set SOURCE_EXTRA to something
>> other than 1 at compile time?  I do not see it listed as an option in the
>> configure documentation, but perhaps I could edit a file, or pass in the
>> flag anyhow?
>>
>
> Roger,
>
> I haven't followed your problems closely (I recall something about datum
> shifts).  The SOURCE_EXTRA only helps with the GDAL warper.  If you wanted
> you could modify the following code in gdal/alg/gdalwarpoperation.cpp
> and recompile:
>
> /* -------------------------------------------------------------------- */
> /*      Allow addition of extra sample pixels to source window to       */
> /*      avoid missing pixels due to sampling error.  In fact,           */
> /*      fallback to adding a bit to the window if any points failed     */
> /*      to transform.                                                   */
> /* -------------------------------------------------------------------- */
>    if( CSLFetchNameValue( psOptions->papszWarpOptions,
>                           "SOURCE_EXTRA" ) != NULL )
>    {
>        nResWinSize += atoi(
>            CSLFetchNameValue( psOptions->papszWarpOptions, "SOURCE_EXTRA"
> ));
>    }
>    else if( nFailedCount > 0 )
>        nResWinSize += 10;
>
>
> Perhaps change the nResWinSize += 10 line to nResWinSize += 100 or
> something
> like that.
>
> Best regards,
> --
>
> ---------------------------------------+--------------------------------------
> I set the clouds in motion - turn up   | Frank Warmerdam,
> warmerdam at pobox.com
> light and sound - activate the windows | http://pobox.com/~warmerdam<http://pobox.com/%7Ewarmerdam>
> and watch the world go round - Rush    | Geospatial Programmer for Rent
>
>
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